Flow restricting device



April 1950v J. H. STRESEN-REUTER 2,502,602

FLOW RESTRICTING DEVICE Filed July 20, 1944 2 Sheets-Sheet l uzazu ow mum oh $522 w mm. m. 7 T mi 92 d5. 3 w m m m2 1 E A m 5 we. H n W j NJ Gm W V April 4, 1950 Filed July 20, 1944 FIG 2 use FIG. 4 I92 I86 2 Sheets-Sheet 2 FIG. 3

Patented Apr. 4, 1950 UNITED STATES PATENT OFFICE Signor, by mesne assignments, to Niles-Bement- Pond Company, West Hartford, Conn, a corpo ration of New Jersey Application July 20, 1944, Serial No. 545,805;

This invention relates'to flow measuring apparatus, and" particularlytoapparatus for meastiring-the flow of air thru a carburetor adapted for'use on an internal combustion-engine.

Acarburetor may be'defined as a device for con-' trolling the fuel-to-air ratio of the charge supplied to the cylinders of an internal combustion engine. In order to control the proportions of the charge, certain types of carburetors now in common use-on aircraftutilize means for measuring the air flow, means for measuring the fuel flow, and means for comparing the air and fuel flows :and forcontrolling the fuel flow so as to correct it if it is: not inthe correct proportion with respect to the air fl'ow.

The most commonly used means for measuring the air flow isa'Venturimeter. This meter is required to measure'the air flow accurately over a much wider range of air flows than isusually required of Venturi meters in other applications. The meter. must measure the air flowaccurately at relatively low engine speeds, and" also at the high engine speeds and power outputs encountered at-take-ofi conditions.

In: addition to. the problems raised because'of the'wide range of air flows which'the Venturimeter is required to measure, additional problems are presented because of the space and weight limitations imposed onan aircraft engine; The air induction System is required to be of the smallest: possible size to admit the quantity of air neeessary'to run'the engine at its maximum power output. Since the small'estpart of the air induction system is the throat of the Venturi meter, it isurequiredthat thecross-sectional area of" the Venturi' throat be suficientlylarge that it will not restrict the air flow so as: to prevent. operationof the engine at'maximum powerz. Ithas been found that: this requires a-Venturi' throat area equal to. at least one-third of the: cro'ssesecti'onal area of the unrestricted portion of the air induction'system. Vifhen theV'enturi throat areaismade equal 13!)!01' greater than OI'IBr-thiBd'O'f thecross sectiumv ofiythe. unrestricted; portion of the air induction system, their the. pressure: differentials set up by" the Venturi meter at. low air flows are so small Claims. (Cl. '7'3213) that the measuring forces. produced do-n-ot change.

paratively moresevere, and the required range over which the Venturi meter must operate increases. The need for a device which will accurately amplify a small pressure differential is consequentlygreat'and rapidly becoming greaten I It is, therefore, anobject of the present inventionto provide improved means for measuring the rate of flow of fluid.

Another object is to provide an improved device of the type shown in the co-pending application of Harold F. 'Iwyman, Serial No. 486,599, filed- May' 11,' 1943 which has matured into Patent Number 2,391,755.

A further object is to provide an improved device which responds to a flow of fluid caused by afirst pressure difierenti-alto produce a higher pressure differential varying with the rate of flow of 'the fluid.

A'further object is to provide improved means for measuring the rate of flow of air thru the induction' system of an internal combustion engine.

Another object is to provide improved means for establishing a pressure differential varying with the rate of fluid flow including an orifice and a draft tube of gradually increasing diameter downstream from the orifice.

Other objects and advantages of my invention will become apparent from a consideration of the appended specification, claims and drawings, in which Figure 1 is a somewhat diagrammatic illustratien of my invention as applied to a carburetor for an internal combustion engine.

Figure 2 is'a cross-sectional View of a preferred form of" pressure differential producing means embodying the principles of my invention, and

Figures 3 and 4 are cross-sectional views of modified forms of devices for producing a pressure differential varying with a rate of fluid flow in accordance with the principles of my invention.

Referring to the drawings, there is shown in Figure 1 a body H] of a carburetor for an aircraft' type internal" combustion engine. Air enters the carburetor body Hi at an inlet i2 and flows thru a Venturi' restriction l4 and a passage l5,

past a'throttle Hi and a. fuel discharge nozzle M to an outlet ZHJ A- supercharger may be provided between the outlet; 20' and the. intake manifold of the. engine; In'ucertain cases the supercharger may be upstream from the inlet l2. or two superchargersmay belusedg. one in each place.

The Venturi' restriction E l produces a pressure difierential between the inlet l2 and thethroat of .the restribtion which varies substantially in accordance. with the square ef the velocity of the The air enters this secondary at 58, a jet system 60, an idle valve I25, a conduit 62, a valve 64 in a second pressure regulator 66, and a conduit 68 to the fuel discharge nozzle IS.

The pressure regulator 54 includes a dia phragm Ill separating a pair of expansible chambers I2 and I4 and connected at its center to the valve 52. A spring I6 biases the valve 52 toward open position. A restriction I8 connects the chambers 12 and I4.

A portion of the fuel entering pressure regulator 54 flows thru chamber I4, restriction I8,

24 interconnecting all the impact tubes, a conduit 26, an orifice 21, a draft tube passage 29, past a valve 38 into a'chamber 40, and then thru a conduit 42 to the throat of Venturi I4.

The orifice 21 is a small cylindrical'passage, which delivers air into the narrow end of the draft tube passage 29 of gradually increasing di-- ameter. A pressure differential is thereby produced between the entrance to the orifice 2! and a point a short distance downstream from its entrance, which is proportional to but greater than the pressure differential between the air inlet I2 and the thoat of Venturi [4. This structure and its function are described more completely below in connection with Figure 2.

The valve 38 is operated by a sealed bellows 44 mounted in the chamber 40. The bellows '44 is fixed at one end, so that the position of the free end, to which valve 38 is attached, varies in accordance with the air pressure in the chamber 40. Bellows 44 is preferably filled with nitrogen or some other suitable temperature responsive fluid, so that the position of valve 38 varies not only with the pressure but also with the temperature of the air in the chamber 40, and hence with the density of that air.

The pressure differential produced by Venturi I4 varies with the velocity of the flowing air, rather than with the mass of air flowing per unit time. Since it is desired to obtain a measure of the mass of air flowing, rather than the velocity of the air, it is necessary to correct the metering apparatus for variations in air density. This is accomplished by the valve 38 and bellows 44. The valve 38 is moved toward open position as the air density increases and toward closed position as the air density decreases. If the volumeof air flowing per unit time thru the passage I5 remains constant and its density decreases, then the mass of air is decreased, but the pressure differential set up by the Venturi I4 remains constant. How-- ever, the movement of valve 38 toward closed position causes the flow of air thru orifice 21' to de-- crease,- so that the pressure drop between the entrance and the center of orifice 21 is decreased to compensate for the decrease in density. The pressure differential set up by'the orifice 21 is thereby made to vary as a function of the mass of air flowing thru the passage I5 rather than its velocity.

The pressure differential across-the orifice 21 is communicated thru conduits 26 and 36 to chambers 28 and 34 located on the opposite sides of a diaphragm 46 in a pressure meter 30. The diaphragm 46 is attached at its center to a valve 48. The force produced by the pressure diifer-- ential at the orifice 2! actsin a downward or closing direction on valve 48.

The fuel enters the carburetor from a fuel pump or other source of fuel under superatmospheric pressure. It flows thru a conduit 59, a valve 52 in a pressure regulator generally indicated at 54, a-

chamber I2, a conduit 80, a chamber 82 in the pressure meter 38, past the valve 48, and thru a conduit 84 to the main air passage I5.

The pressure meter includes a diaphragm 86 separating the chambers 34 and 82 and a diaphragm 88 separating the chamber 28 from a fourth expansible chamber 90. The valve 48 is biased toward closed position by a spring 92.

.The chamber 90 is connected thru a conduit 94. to the fuel conduit 62 downstream from the jet system 60. The pressure in chamber 99 is therefore the same as that in the fuel line downstream is determined by the balance between the spring,

from the jet system. The pressure in chamber 82 is the same as that in chamber I2 of pressure regulator 54.

The position of diaphragm I9 and valve 52 16 plus the pressure in chamber I2 acting in a valve opening direction and the pressure in chamber I4 acting in a valve closing direction. If the,

balance between these forces is upset, the diaphragm I0 and valve 52 move until the balance is.

restored. Therefore the pressure in chamber I2 is a measure of the pressure in chamber I4, which is substantially the same as the pressure on the, upstream side of the jet system 60. For any given constant cross-sectional area of the fuel passages thru the jet system 60, the pressure differential across it is a measure of the fuel flow thru it. This pressure differential, or rather a smaller pressure differential which is a measure I of the pressure differential across the jet system,

is applied thru the diaphragms 86 and 88 of pressure meter 30 to the valve 48, on which it acts 1 an opening direction.

From the foregoing, it may be seen that the.

valve 48 is positioned in accordance with the balance between two forces, one of which varies in accordance with the mass of air entering thecarburetor, and the other in accordance with the mass of fuel entering the carburetor.

- thermore, the valve 48 controls the mass of fuel entering the carburetor, since it controls the pressure in chamber 82. The pressure in the chamber 82 is transmitted to chamber I2 of pressure regulator 54 where it controls the position of valve 52 and hence the pressure on the upstream side of the jet system 69.

The pressure regulator 66 operates to maintain a substantially constant pressure on the downstream side of the jet system 68 and thereby to prevent variations in pressure at the fuel dis system and affecting the fuel flow.

I valve 64 toward closed position. The chamber 96 is connected thru a conduit I84 to the conduit, 26 and thence thru thepassage 24 and impact The pressure regulator 66 includes a pair eXpansible chambers 96 and 9B separated by-a,

flexible diaphragm I00, which is attached at its center to the valve 64. A-spring I62 biases the Furtubes=-22to; the air entrance t2. The chamber 98 is connected to the conduitt m.

. The mixturecontrol: .58 includes a disc. valves I06 fixed on. a. shaft lfla. The disc valve ILOE controls the flow of fuel thru ports opening into. conduits Hfl 'and I I2 which. Ieadsintouthe jet. system 61!; When the. discl I18 is. in thei. position illustrated full lines in the drawing-,iuel can? flow' to the jet system'only thru the.- conduit I Ill-.5. Thistullt line position of the. disc. valve lillG is known asthe lean position of the mixture. con-. trol 58. When the disc val've, N16: i in. the. dotted line position shown in the drawing,. the-.fuel.can.1 flow "thru both the. conduits: I1 Iifi and I 82. The dotted line. position ofi'disc: .valve.-. "Minis termedi the 'ric positionsof' the mixture control'." The. valved. can. also be moved to; a ,-.cut.-oi"f position wherein: it: cuts. off the flow" thruboth: conduits I. I and H2.

The. conduit. lllflwconducts. fuel eitherathru a' fixedrestriction orjet H4, or thru a restriction! HE controlled. by a. valve M8 biasedto closed position by a. spring. I 2.0. The conduit. I I;-Z'-conducts fuel to a fixed restriction. I2 2. Fueltflow-i-ng-tlniua the. restrictions H6: and; I322 also. flows thru another restriction I24. which limits: the/total. flow thru restrictions [16. and: [2h

The. valve I138; is: normally closed, butopens at; high pressure differentials. across/the: .j'et sys-- tem to. increase. the.- iuel-to-air ratio.- under heavy load conditions..

, At; very lowair flows, such. as are encountered; undenidling conditions, the pressure differential; set: up: by the Venturi I4? tends to; be. erratic: and:

is; not a-reliable' indication of thee'volume: of; air

entering the engine. Provision isma'de. tQ'GQYL-t. trol: the: fueli-fiow' directly in accordance: with the: throttle: position atzsuch. times. The spring 9 2: in. the pressure meter 311:.acts: on'val-ve: 48 ir-ra. closing direction; .When the. differential pressure: acting, on. diaphragmid is; small, as: under flow-conditions; .thespringi. 9.2: becomes the. predominating force: actingorr valyedfli; A clos-e ing movement of valve 48 causes an increase: in: the: fiuel flow thru the: main'fuelrl'lne,- since the closure. of, valve48 increases the pressure .inw chamber--82 of pressure meter; 3.0.82Ildii1l8116flil11 chamber I2 of pressure regulator 54;; Furthermore the spring 16; "of; pressure.- -.regu1ator 5.41 biases: valve 52 man. opening. or fuel fiowi-ncrease ing direction.

. The idle valve I-- is pivotally'attachedi:to: a; lever I 2-:8,, whose opposite end; .is connectedibya; I39 to an. arm I32- fixed onatheshait Hi4 throttle I6-., The: idle Valve; is normally wide open. when: the throttle is bQYOHdlafIaHgBZiOi T po;-.- sitions near its closed position, usually termed the. idling ranges- As the; throttle. moves into; the: idling range. thereby decreasing the-air flow, the-:id-le valve [zit-moves: toward closed; position... At; the; same; time, the springs 92 and. 1:6 cancer operation. of valve 52: int-an opening directionr The; valve: 52; is: thereby opened sufficiently so" that its; restrictive efiect on-the fuel flow is. less. than: that: of the idle .valve-I2 5.v Therefore; the fiuel flow under idling conditions is controlled primarily by the valvel25; in accordance with the position. of. the throttle, and'notby".the:..pressure meter, 3.0 in-accordance, with themassof air em tering the engine..-

While I have illustrated a-particular typeot carburetor, it will be appreciated by those skilled inthe art thatmy'inventionmay'be appliedswith. equal facilityto other types oi'carburetors- The. carburetor illustratedimay; for example; be; modiparallel lines.

6; fled. by omitting the pressure regulator 54; and placing the valve, 4'I8 of. the pressure meter 30 directly in the fuel line. between the pump and the mixture control 58.

Figure 2 There. is. shown in. Figure; 2: an orifice and draft tube. construction; similar to. that shown more diagrammatically at and: 2:9 in Figure 1.. The construction shown in- Figure 2 consists of two pieces, an orifice-plate I and a. draft tube: 152. The, upstream surface of: the. orifice plate I50 is conical, the orifice 2'! opening at the center of the: cone. and forming a. short. cylindrical passage thru the plate I511. .The downstream side of the orifice plate IE0 is countersunk about the orifice 21', as indicated at I54.

The draft tube I52 is provided with upper and lower mounting-flanges I56 and I58. The upper end of the tube I52 is provided with an upwardly projecting peripheral flange I66 to receive and locate the orifice'plate I50. The upper surface of the tube I52 is recessed to' form a chamber I'62' under the orifice plate I50. At the center of the chamber I62, the upper end of tube I52 is provided witha conical projection I64 which extends into, but does not contact, the countersunk portion- I54 of the orifice plate I50. The tube I 52 is provided with a central cylindrical bore I66 which extends downwardly a short distance fromthetip of'theconical projection I'M. The cylindrical bore [66 opens intothe draft tube passage 29, of gradually increasing diameter, which extends downwardly thru the tube I 52 to its lower end. In other Words, the restriction device of Fig. 2 may be said to consist of a cylindri'cal passage (including both orifice 2T and bore- I 66) leading to a flaring draft tube 29, with a lateral opening into the cylindrical passage to permit an external connection of a device functioning'in proportion tothe pressure therein.

The conical upper surface of the plate I provides a sharp edge for the orifice 21' so that the air entering that orifice flows in substantially This parallel flow "continues for a short distance before-the usual disturbing effects due to the surface of the tube cause an uneven velocity distribution inthe orifice. The small opening between the upper end of the conical" projection I64 and the countersunk portion- I54 of the *plate- I5Il= provides a means for communicating the pressure within the orifice Z'I-at' a point therein where the velocity distributi'on is uniform; This pressure is communicated thru the space to the aperture I62, which is in turn connected thrupassages I68 to the conduit 36' of Figure 1. The space on the upstream s de of'orifice 2 1 is connected to the conduit 26 of Figure 1.

It has been found" essential, in order to pro-- vide uniform velocity distribution thru a flow pressure difierential responsive device of the type shown in Figure 2, to make the distance between the entrance to the orifice and the point at which the pressure is measured equal to not more than V of the internal diameter of the orifice. The minimum dimension which may be used isdetermined more by the characteristics. at the materiak and themed for rigidity-rather than. by: an-y'l'a'w' or characteristic of fluid flow; For example z, inyoneembodiment of: my invention, the. internal diameter oizthe; orifice is approximately .102: inch, I and; the distance. between. the orifice-entrancesand. the point at. which the; pres.- s-ure-is measured withirr'thapassaga ism-0Z8 incht 7 The width of the opening thru the walls of the passage is approximately .003 inch.

Figure 3 There is illustrated in Figure 3 a modified form of orifice and draft tube construction which may be used in place of that shown in Figure 2. The form shown in Figure 3 differs from that in Figure 2 chiefly in that the orifice plate is provided with an inwardly tapering conical surface as contrasted to the projecting conical surface of Figure 2. The draft tube I18 is also provided with a countersunk portion at its upper end instead of the projecting cone I64 of Figure 2.

Figure 4 The form of the device shown in Figure 4 has three pieces, a first orifice plate I86, a second orifice plate I88, and a draft tube I90. The construction of the draft tube I90 is substantially the same as that of the draft tube I18 of Figure 3. The second orifice plate I88 has the orifice formed with its internal diameter decreasing in the direction of flow along a substantially parabolic curve, somewhat similar to the entrance to a Venturi. The orifice plate I86 is in the form of a cap which is internally threaded so that it may be screwed on to external threads on tube I96. The orifice I92 thru the plate I86 is a short straight-sided cylindrical orifice. The device of Figure 4 does not have the dimensional limitations of the device shown in Figure 2, but it is more complicated structurally.

While I have illustrated and described certain preferred embodiments of my invention, other modifications thereof will readily occur to those skilled in the art, and I therefore intend my invention to be limited only by the appended claims.

I claim as my invention:

1. A flow restricting device for use in apparatus for measuring flow through a passage, comprising an elongated, generally tubular member forming a portion of said passage, said member having a central conical projection at its upstream end and a bore extending axially of said projection, said bore comprising a first portion of constant diameter and a second portion adjoining the downstream end of said first portion and havin a diameter gradually increasing in the direction of flow, and a plate member extending across said passage upstream from said tubular member, said plate member having its upstream surface in the form of a projecting truncated cone, and a central aperture of substantially the same diameter as said first portion of the bore in said tubular member, the downstream surface of said plate member being countersunk around said aperture to receive the conical projection on the upstream end of said tubular member, said members having cooperating surfaces for establishing their relative locations so that the conical projection on said tubular member extends into but does not engage the countersunk downstream surface of said plate member, with said aperture aligned with said bore, so as to form an opening between said countersunk surface and said conical projection.

2. A flow restricting device for use in apparatus for measuring flow through a passage, comprising an elongated, generally tubular member forming a portion of said passage, said member having an axially extending bore comprising a first air conduit of constant diameter and a second air conduit adjoining the downstream end of said first conduit and having a diameter gradually increasing in the direction of flow, and-a plate member extending across said passage upstream from said tubular member, said plate member having a cylindrical orifice of substantially the samediameter as said first conduit, the thickness of said plate member at said orifice being less than one-third of the diameter of said,

orifice, said members having cooperating surfaces for establishing their relative locations so that the upstream end of said bore is spaced from the downstream end of said orifice, thereby forming a lateral opening into said passage between said members.

3. A flow restricting device for use in apparatus for measuring fiow through a passage, comprising an elongated, generally tubular member forming a portion of said passage, said member having a central conical projection at its upstream end and a bore extending axially of said projection, said bore comprising a first portion of constant diameter and a second portion adjoining the downstream end of said first portion and having a diameter gradually increasing in the direction of flow, and a plate member extending across said passage upstream from said tubular member, said plate member having its upstream surface in the form of a projecting truncated cone, and a central aperture of substantially the same diameter as said first portion of the bore in said tubular member, the thickness of said plate member at said aperture being less than one-third of the diameter of said aperture, the downstream surface of said plate member being countersunk around said aperture to receive the conical projection on the upstream end of said tubular member, said members having cooperating surfaces for establishing their rela-' tive locations so that the conical projection on said tubular member extends into but does not engage the countersunk downstream surface of said plate member, with said aperture aligned with said bore, so as to form an opening between said countersunk surface and said conical projection.

- 4. A flow restricting device for use in apparatus for measuring flow through a passage, comprising structure having an elongated, generally tubular member forming a portion of said passage, said member having at its upstream end a. conical projection about a bore extending axially thereof, said bore comprising a first portion of constant diameter and a second portion adjoining the downstream end of said first portion and having a diametergradually increasing in the direction of flow, and a plate member extending across said passage upstream from said tubular member, said plate member having an outwardly tapering conical surface on its upstream side and a central aperture of substantially the same diameter as said first portion of the bore in said tubular member, the downstream surface of said plate member being countersunk around said aperture to admit the conical projection on the up stream end of said tubular member, said members having cooperating surfaces for establishing their relative locations so that the projection on said tubular member extends into but does not engagethe countersunk surface of said plate member, with said aperture aligned with said bore, so as to form an opening between said countersunk surface and said projection.

5. Fluid flow pressure differential responsive means, comprising structure having a passage for the flowing fluid, there being a restriction in saidpassage having a cylindrical bore with a 9 sharp-edged opening and a length substantially greater than its diameter, and a draft tube of gradually increasing diameter abutting said restriction and receiving fluid from said cylindrical bore, and means responding to the difierence between the pressure in said passage at the upstream entrance to said opening and the pressure at a point in said bore spaced from said entrance by a distance equal to not more than one-third of the diameter of said opening.

JOHN H. STRESEN-REUTER.

REFERENCES CITED The following references are of record in the file of this patent:

Number Number 10 UNITED STATES PATENTS Name Date Ferris May 30, 1905 Bacharach June 13, 1922 Pardoe Mar. 15, 1932 Engel Nov. 13, 1934 Hess Oct. 26, 1943 Udale May 23, 1944 Mock Oct. 24, 1944 Mock Oct. 24, 1944 FOREIGN PATENTS Country Date Great Britain Dec. 4, 1919 

